Diversity of Ruminococcus strains: a survey of genetic polymorphisms and plant digestibility

Twenty-three strains of Ruminococcus isolated from ruminants were assessed for digestive ability on different plants and purified cellulose. Genetic d iversity was assessed by ERIC, REP and 16-23S rDNA spacer polymorphisms. Al l ruminococci could be typed by ERIC, REP or 16-23S rDNA spacer, but all th ree typing methods had to be used in concert to differentiate closely relat ed strains. Digestibility of lucerne (Medicago sativa), rhodes grass (Chlor is gayana) and spear grass (Heteropogon contortus) were assessed. Dry matte r (DM) digestibility was highly correlated (> 0.93) with neutral detergent fibre (NDF) digestibility, but cellulose disc digestibility was a poor indi cator of DM and NDF digestibility. Studies demonstrate the wide variation i n ability of ruminococci to digest forages, and some recently isolated stra ins (Y1, LP-9155, AR67, AR71 and AR72) were superior to reference strains ( FD-land Ra8). Multivariate analysis showed that groupings derived from geno typing data closely resembled those determined by digestibility data. This study indicated that ruminococci are diverse in digestive ability and genot ype, and this diversity suggests that there may be highly fibrolytic strain s in nature that could be utilized for animal production.